President Obama, looking to win the public relations battle over a looming government shutdown, took his case directly to voters this weekend.

In his regular radio address Saturday, the president told Americans that an "extreme faction" of the House GOP is risking an economic calamity to torpedo his health care law.

"In the next couple days, these Republicans will have to decide whether to join the Senate and keep the government open, or create a crisis that will hurt people for the sole purpose of advancing their ideological agenda," Mr. Obama said.

Mr. Obama's supporters followed up Sunday on Facebook and Twitter with a daylong stream of posts citing the crisis in fundraising appeals and urging backers to contact lawmakers and weigh in on behalf of the Affordable Care Act — the comprehensive health care law that Republicans have sought to defund.

But a top House Republican said the president is ignoring a "golden opportunity" to address Washington's spending and debt problems.

"He wants to take the easy way out — exactly the kind of foolishness that got us here in the first place," said Rep. Cathy McMorris Rodgers, Washington Republican, in the GOP's weekly address.

Congress and the president must agree on a short-term spending bill by midnight Monday to keep the federal government running.

Enrollment in new health-insurance exchanges is set to start Tuesday, just as the government would close for business — a deadline noted by the president in his address.

"The Affordable Care Act is one of the most important things we've done as a country in decades to strengthen economic security for the middle class and all who strive to join the middle class," Mr. Obama said. "That's also one of the reasons it's so disturbing that Republicans in Congress are threatening to shut down the government — or worse — if I don't agree to gut this law."

The president also criticized Republicans for seeking to negotiate with him over a proposal to raise the nation's borrowing limit. Without an increase in the debt ceiling by mid-October, the government would default on some of its obligations.

"Unfortunately some Republicans have suggested that unless I agree to an even longer list of demands — not just gutting the health care law, but things like cutting taxes for millionaires or rolling back rules on big banks and polluters — they'll push the button, throwing America into default for the first time in history and risk throwing us back into recession," Mr. Obama said. "No one gets to hurt our economy and millions of innocent people just because there are a couple laws you don't like. It hasn't been done in the past, and we're not going to start doing it now."

But Mrs. McMorris Rodgers noted that presidents have routinely negotiated with lawmakers in the past when reaching agreements to increase borrowing, from Ronald Reagan to Bill Clinton to Mr. Obama himself in 2011.

"Every major deficit reduction effort of the last 30 years has been tied to the debt limit. This time should be no different," she said.

"Unfortunately, the president is now demanding that we increase the debt limit without engaging in any kind of bipartisan discussions about addressing our spending problem."

She said House Republicans have put forward a plan that "contains cuts and real reforms to build a 21st century economy — from approving the Keystone pipeline and fixing our outdated tax code to delaying the president's health care law."